For example, Japanese Patent Application Publication 2008-42999 describes a power supply apparatus that uses a solar battery or a fuel battery as a power source device. In the power supply apparatus, the voltage of electric power generated in the power source device is converted through a first DC/DC converter circuit, and the electric power is then supplied to a DC power source line (e.g., DC bus line). Thus, a secondary battery connected to the DC power source line is electrically charged. Further, a second DC/DC converter circuit is connected between a DC power supply line to which an electric load device is connected and the DC power source line. Therefore, the electric power generated from the power source device is supplied to the electric load device via the first DC/DC converter circuit and the second DC/DC converter circuit.